A composite photocatalyst for removing methylene blue and a preparation method and application thereof

Abstract

The application relates to the field of photocatalysis, in particular to a composite photocatalyst for removing methylene blue and a preparation method and application thereof. The preparation method of the composite photocatalyst for removing methylene blue comprises the following steps: mixing a mixed solvent containing choline chloride, ethylene glycol and water, a nickel source, an iron source and citric acid, and performing a complexing reaction, then adjusting the pH value of the reaction system, and performing a self-propagating reaction by heating to obtain a precursor; the precursor is calcined to obtain the composite photocatalyst; the main components of the composite photocatalyst include NiFe2O4, alpha-Fe2O3 and Ni3Fe. The composite photocatalyst with the main components of NiFe2O4, alpha-Fe2O3 and Ni3Fe can be obtained by adopting the method, the composite photocatalyst can overcome the shortcomings of pure nickel ferrite and alpha-Fe2O3 as photocatalysts, and the photocatalytic capacity is further improved.

Description

Technical Field

[0001] This invention relates to the field of photocatalysis technology, and more specifically, to a composite photocatalyst for removing methylene blue, its preparation method, and its application. Background Technology

[0002] Methylene blue, an organic dye, is widely used in the textile industry. Due to its inherent toxicity and extremely high solubility in wastewater, it has become a major source of wastewater pollution, seriously impacting human health, the ecological environment, and water quality.

[0003] Photocatalysis can effectively degrade many structurally stable organic pollutants and has become one of the pollution control technologies that have received attention both domestically and internationally. Its application research in environmental protection and governance began in the 1970s. TiO2, as a typical photocatalyst, has certain limitations. TiO2 has a band gap of 3.2 eV, and it can only generate electron-hole pairs when irradiated with light of wavelengths less than 388 nm. This results in a very low solar energy utilization rate for TiO2, less than 5% of solar radiation.

[0004] Hematite (α-Fe₂O₃) is an environmentally friendly n-type semiconductor material with a band gap (Eg) of approximately 2.1 eV and a visible light absorption threshold of around 600 nm, enabling it to absorb most visible light and effectively utilize sunlight. Furthermore, α-Fe₂O₃ boasts advantages such as abundant raw materials, low cost and availability, good stability, and non-toxicity. However, α-Fe₂O₃ also suffers from drawbacks including low visible light absorption coefficient, severe electron-hole recombination, poor conductivity, low carrier mobility, and short photogenerated hole diffusion length. Therefore, it is necessary to broaden its photoresponse range and improve its photocatalytic performance by constructing nanostructures or heterojunctions.

[0005] Spinel-type nano-ferrites are chemically stable and have demonstrated excellent catalytic performance as catalysts. They also offer advantages such as reusability, high selectivity, and low reaction temperature. NiFe₂O₄, with a band gap of approximately 2.2 eV, is a typical spinel semiconductor. It can be excited at a wavelength of 540 nm under light irradiation and exhibits a wide absorption range for sunlight. However, pure nickel ferrites possess high magnetic properties, and the particles are easily attracted to each other due to magnetic interactions, thus reducing the specific surface area and consequently decreasing the light utilization rate.

[0006] Therefore, it is of great significance to provide a catalyst that can overcome the shortcomings of pure nickel ferrite and α-Fe2O3 as photocatalysts and further improve the photocatalytic ability.

[0007] In view of this, the present invention is hereby proposed. Summary of the Invention

[0008] The primary objective of this invention is to provide a method for preparing a composite photocatalyst for removing methylene blue. This method yields a composite photocatalyst whose main components include NiFe2O4, α-Fe2O3, and Ni3Fe. This composite photocatalyst overcomes the shortcomings of using pure nickel ferrite and α-Fe2O3 as photocatalysts, thereby further enhancing the photocatalytic activity.

[0009] The second objective of this invention is to provide a composite photocatalyst for removing methylene blue.

[0010] A third objective of this invention is to provide an application of the above-mentioned composite photocatalyst in the photocatalytic removal of organic pollutants.

[0011] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0012] This invention first provides a method for preparing a composite photocatalyst for removing methylene blue, comprising the following steps:

[0013] A mixed solvent containing choline chloride, ethylene glycol and water, a nickel source, an iron source and citric acid were mixed and subjected to a complexation reaction. Then the pH value of the reaction system was adjusted and heated to carry out a self-propagating reaction to obtain the precursor.

[0014] The precursor is calcined to obtain the composite photocatalyst;

[0015] The main components of the composite photocatalyst include NiFe2O4, α-Fe2O3 and Ni3Fe.

[0016] The present invention further provides a composite photocatalyst prepared by the method for preparing the composite photocatalyst for removing methylene blue, wherein the main components of the composite photocatalyst include NiFe2O4, α-Fe2O3 and Ni3Fe.

[0017] The present invention also provides the application of the composite photocatalyst in the photocatalytic removal of organic pollutants.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] (1) The method for preparing a composite photocatalyst excluding methylene blue provided by the present invention can obtain a composite photocatalyst whose main components include NiFe2O4, α-Fe2O3 and Ni3Fe. This composite photocatalyst can overcome the shortcomings of pure nickel ferrite and α-Fe2O3 as photocatalysts, and further improve the photocatalytic ability.

[0020] (2) The composite photocatalyst prepared by the method of preparing the composite photocatalyst for removing methylene blue provided by the present invention has a good treatment effect on methylene blue dye, with a high removal rate and a short removal time.

[0021] (3) The composite photocatalyst prepared by the method of preparing composite photocatalyst excluding methylene blue provided by the present invention has strong magnetic properties, can be recycled and reused multiple times, and is low in cost, environmentally friendly and energy-saving.

[0022] (4) The composite photocatalyst prepared by the method of preparing the methylene blue removal composite photocatalyst provided by the present invention has a basically unchanged removal rate when it is reused multiple times. Attached Figure Description

[0023] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0024] Figure 1 The XRD pattern of the composite photocatalyst provided in Example 2 of this invention;

[0025] Figure 2 The graph shows the change in the removal rate of methylene blue solution by the composite photocatalyst prepared in Example 1 of this invention as a function of treatment time.

[0026] Figure 3 The graph shows the change in the removal rate of methylene blue solution by the composite photocatalyst prepared in Example 7 of this invention as a function of treatment time.

[0027] Figure 4 The graph shows the change in the removal rate of methylene blue solution by the composite photocatalyst prepared in Example 8 of this invention as a function of treatment time.

[0028] Figure 5 The graph shows the change in the removal rate of methylene blue solution by the composite photocatalyst prepared in Example 9 of this invention as a function of treatment time.

[0029] Figure 6 The graph shows the change in the removal rate of methylene blue solution by the composite photocatalyst prepared in Comparative Example 1 of this invention as a function of treatment time.

[0030] Figure 7 The graph shows the change in the removal rate of methylene blue solution by the composite photocatalyst prepared in Comparative Example 2 of this invention as a function of treatment time.

[0031] Figure 8 The graph shows the change in the removal rate of methylene blue solution by the composite photocatalyst prepared in Comparative Example 3 of this invention as a function of treatment time.

[0032] Figure 9This is a comparison of the methylene blue removal rates of the composite photocatalyst provided in Example 2 of the present invention during the first and third repeated recovery processes, as a function of treatment time.

[0033] Figure 10 This is a schematic diagram of the composite photocatalyst provided in Example 2 of the present invention during the third recovery process;

[0034] Figure 11 The image shows the hysteresis loop diagram of the composite photocatalyst prepared in Example 2 of this invention. Detailed Implementation

[0035] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0036] Unless otherwise specified, in this invention, terms such as "first aspect," "second aspect," "third aspect," and "fourth aspect" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, terms such as "first," "second," "third," and "fourth" serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0037] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0038] Unless otherwise specified, in this invention, "one or more" or "at least one" refers to any one, any two, or any two or more of the listed items. "Several" refers to any two or more.

[0039] In a first aspect, the present invention provides a method for preparing a composite photocatalyst capable of photocatalytically removing methylene blue, comprising the following steps:

[0040] A mixed solvent containing choline chloride, ethylene glycol, and water, along with a nickel source, an iron source, and citric acid, is mixed and subjected to a complexation reaction. After a period of time, the pH of the reaction system is adjusted, and the mixture is heated to carry out a self-propagating reaction. Once the reaction is complete, the precursor is obtained.

[0041] Among them, choline chloride and ethylene glycol eutectic solvents have special physicochemical properties and electrochemical windows, especially good solubility for metal ions and metal oxides, and can be used as solvents and templates in the synthesis of materials.

[0042] Citric acid plays the role of a complexing agent and a regulator. Specifically, the functions of citric acid mainly include the following aspects: (1) Buffering effect: As an acidic substance that can provide buffering in aqueous solution, citric acid can help regulate the pH of the reaction system, so that the resulting gel is in a suitable pH range, which is conducive to the formation of sol and the stability of gel. (2) Coordination complexing effect: The carboxyl group in citric acid can coordinate complex with metal ions to form stable complexes. In the sol-gel method, citric acid can act as a complexing agent to form complexes with metal ions in metal salts, which helps to stabilize metal ions and control the formation of gel. (3) Control of grain growth: Citric acid can affect the activity of sol by complexing with metal ions, thereby affecting the spatial network structure of gel, and thus affecting the nucleation and grain growth of intermediate phase and product during precursor calcination, which is beneficial to the regulation of the microstructure of materials.

[0043] In summary, citric acid plays a role in the sol-gel self-propagating process mainly through its function as a buffer, complexing agent, and grain control. It helps to regulate reaction conditions, stabilize the formation process of sol and gel, and influence the microstructure and properties of the material.

[0044] The purpose of adjusting the pH value of the reaction system is to regulate the ionization state or molecular structure of solute molecules during the sol-gel formation process, thereby promoting the formation of sol-gel.

[0045] The precursor is calcined and then cooled to obtain the composite photocatalyst.

[0046] The main components of the composite photocatalyst include NiFe2O4, α-Fe2O3 and Ni3Fe.

[0047] Among them, nickel-iron alloy (Ni3Fe) is magnetic, and the presence of Ni can promote electron transfer, thereby enhancing the photocatalytic degradation of pollutants.

[0048] In this invention, choline chloride and ethylene glycol act as both solvents and participate in the reaction. The roles of choline chloride and ethylene glycol include: (1) making the metal ions more evenly dispersed during the sol and gel process; (2) reacting with the metal ions during the self-propagation process to generate organometallic compounds, which make the metal ions more evenly dispersed in the precursor; (3) during the precursor calcination process, the intermediate phase reaction of the organometallic compounds causes the product to not only generate spinel ferrite, but also α-Fe2O3 and Ni3Fe at the same time; (4) during the precursor calcination process, the decomposition reaction of the organometallic compounds releases heat, which accelerates the reaction process.

[0049] This invention utilizes a sol / gel-self-propagating method to prepare a precursor using a mixture containing choline chloride, ethylene glycol, and water as a solvent. The precursor is then calcined at high temperature to obtain a composite photocatalyst. Its main components include NiFe₂O₄, α-Fe₂O₃, and Ni₃Fe. This photocatalyst can be used to treat methylene blue wastewater. This method solves the problems of high energy consumption, demanding experimental requirements, complex operation, secondary pollution, and difficult recovery associated with traditional photocatalyst processes.

[0050] The preparation method provided by this invention is simple, has low raw material cost, is suitable for large-scale production, has high added value, and the resulting composite photocatalyst has a good treatment effect on methylene blue dye, with high removal rate and short removal time.

[0051] Furthermore, the composite photocatalyst prepared by this invention has strong magnetic properties, can be recycled and reused multiple times (NiFe2O4, α-Fe2O3 and Ni3Fe can all be recycled), has low cost, is environmentally friendly and energy-saving, is easy to operate, and can be applied to the treatment of colored dye wastewater.

[0052] In some specific embodiments, choline chloride and ethylene glycol are first mixed evenly, then mixed evenly with water, and then an iron source and a nickel source are added. After a period of time, citric acid is added to carry out a complexation reaction. After a period of reaction, an alkaline solution, such as ammonia, is added to adjust the pH value of the reaction system to obtain a sol. The sol is then heated to gradually form a gel, and the gel is heated again to obtain a precursor through self-propagation. After calcining the precursor and cooling, a composite photocatalyst is obtained.

[0053] To further improve the treatment effect of composite photocatalyst on methylene blue dye, increase the removal rate, and shorten the removal time, this invention has optimized the following parameters: the ratio of choline chloride, ethylene glycol, and water in the mixed solvent; the molar ratio of nickel and iron; the pH value of the reaction system; the amount of citric acid used; and the temperature and time during the preparation process.

[0054] In some specific embodiments, the molar ratio of choline chloride to ethylene glycol in the mixed solvent is 0.5–1.5:1.5–2.5, including but not limited to any one of 0.5:1.5, 1:1.5, 1.5:1.5, 0.5:2, 1:2, 1.5:2, 0.5:2.5, 1:2.5, 1.5:2.5, or any range between two of them.

[0055] In some specific embodiments, the ratio of the sum of the volumes of choline chloride and ethylene glycol to the volume of water in the mixed solvent is 18-27:3-12, including but not limited to any one of the following values ​​or any range between two: 18:3, 20:3, 22:3, 25:3, 27:3, 18:5, 20:5, 22:5, 25:5, 27:5, 18:8, 20:8, 22:8, 25:8, 27:8, 18:10, 20:10, 22:10, 25:10, 27:10, 18:12, 20:12, 22:12, 25:12, and 27:12.

[0056] In some specific implementations, the pH value of the reaction system is adjusted to a value of 7 to 10, including but not limited to a point value of any one of 7, 7.5, 8, 8.5, 9, 9.5, and 10, or a range between any two.

[0057] In some specific embodiments, the molar ratio of iron in the iron source to nickel in the nickel source is 1.6 to 2.9:1, including but not limited to any one of 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, and 2.9:1, or any range between the two.

[0058] In some specific embodiments, the ratio of the molar amount of citric acid to the sum of the molar amounts of iron in the iron source and nickel in the nickel source is 1 to 1.5:1, including but not limited to the point value of any one of 1:1, 1.2:1, 1.4:1, 1.5:1 or the range between any two.

[0059] In some specific embodiments, the temperature of the complexation reaction is 30 to 80°C, including but not limited to any one of 30°C, 40°C, 50°C, 60°C, 70°C, and 80°C, or any range between two of them.

[0060] In some specific embodiments, the complexation reaction time is ≥20 min, including but not limited to any one of 20 min, 30 min, 40 min, 50 min, 60 min, 120 min, 180 min, 240 min, and 300 min, or any range between two of them.

[0061] In some specific embodiments, the calcination temperature is 400 to 900°C; including but not limited to any one of 400°C, 500°C, 600°C, 700°C, 800°C, and 900°C, or a range between any two.

[0062] In some specific embodiments, the calcination time is ≥1h, including but not limited to any one of 1h, 2h, 3h, 4h, 6h, 8h, 10h, 12h, 15h, 20h, and 24h, or any range between two of them.

[0063] In some specific implementations, the nickel source includes, but is not limited to, nickel-containing compounds such as nickel nitrate.

[0064] In some specific implementations, the iron source includes iron-containing compounds, such as ferric nitrate, but is not limited to these.

[0065] Secondly, the present invention provides a composite photocatalyst prepared by the above-described method for preparing a composite photocatalyst for removing methylene blue, wherein the main components of the composite photocatalyst include NiFe2O4, α-Fe2O3 and Ni3Fe.

[0066] It is understood that the composite photocatalyst provided by this invention can remove methylene blue, but is not limited to removing methylene blue.

[0067] Thirdly, the present invention provides the application of the above-mentioned composite photocatalyst in the photocatalytic removal of organic pollutants.

[0068] In some specific embodiments, the organic pollutant includes methylene blue, and the composite photocatalyst has a removal rate of ≥70% for methylene blue solutions with a concentration ≤30mg / L, including but not limited to point values ​​of any one of 70%, 75%, 80%, 85%, 90%, 95%, and 99%, or a range between any two.

[0069] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0070] Example 1

[0071] The preparation method of the composite photocatalyst for removing methylene blue provided in this embodiment includes the following steps:

[0072] Choline chloride and ethylene glycol were mixed at a molar ratio of 1:2 and stirred until homogeneous. Then, the prepared choline chloride-ethylene glycol mixture was mixed with water at a volume ratio of 21:9 (i.e., the sum of the volumes of choline chloride and ethylene glycol to the volume of water was 21:9) to obtain a mixed solvent. 2 mol of ferric nitrate and 1 mol of nickel nitrate were added to a total volume of 30 mL of the mixed solvent and stirred. Then, 3 mol of citric acid was added and the mixture was stirred at 65 °C to initiate a complexation reaction. The pH of the reaction system was adjusted to 8 with ammonia, and the resulting sol was heated to gradually form a gel. The gel was dried and allowed to self-propagate, yielding the precursor. The precursor was calcined at 700 °C for 3 h to obtain the composite photocatalyst.

[0073] Example 2

[0074] The preparation method of the composite photocatalyst for removing methylene blue provided in this embodiment is basically the same as that in Example 1, except that the volume ratio of choline chloride-ethylene glycol to water is replaced with 24:6.

[0075] like Figure 1 The image shown is the XRD pattern of the composite photocatalyst prepared in this embodiment. Figure 1 It can be seen that the main components of the composite photocatalyst prepared in this embodiment are NiFe2O4, α-Fe2O3 and Ni3Fe.

[0076] The BET data of the composite photocatalyst were measured using a Micromeritics 3020 fully automated surface area and porosity analyzer, and the average particle size was found to be 38 nm.

[0077] Example 3

[0078] The preparation method of the composite photocatalyst for removing methylene blue provided in this embodiment is basically the same as that in Example 2, except that the molar ratio of choline chloride and ethylene glycol is replaced with 1:1.5.

[0079] Example 4

[0080] The preparation method of the composite photocatalyst for removing methylene blue provided in this embodiment is basically the same as that in Example 2, except that the molar ratio of choline chloride and ethylene glycol is replaced with 0.5:2.5.

[0081] Example 5

[0082] The preparation method of the composite photocatalyst for removing methylene blue provided in this embodiment is basically the same as that in Example 2, except that the molar ratio of choline chloride and ethylene glycol is replaced with 1.5:1.5.

[0083] Example 6

[0084] The preparation method of the composite photocatalyst for removing methylene blue provided in this embodiment is basically the same as that in Example 2, except that the molar amount of citric acid is replaced with 4 mol.

[0085] Example 7

[0086] The preparation method of the composite photocatalyst for removing methylene blue provided in this embodiment is basically the same as that in Example 2, except that the calcination temperature is replaced with 600℃.

[0087] Example 8

[0088] The preparation method of the composite photocatalyst for removing methylene blue provided in this embodiment is basically the same as that in Example 2, except that ammonia is used to adjust the pH of the reaction system to 7.

[0089] Example 9

[0090] The preparation method of the composite photocatalyst for removing methylene blue provided in this embodiment is basically the same as that in Example 1, except that ammonia is used to adjust the pH of the reaction system to 9.

[0091] Example 10

[0092] The preparation method of the composite photocatalyst for removing methylene blue provided in this embodiment is basically the same as that in Example 1, except that the calcination time is replaced with 4 hours.

[0093] XRD analysis revealed that the main components of the composite photocatalysts prepared in Examples 1 to 10 were NiFe2O4, α-Fe2O3, and Ni3Fe.

[0094] Comparative Example 1

[0095] The preparation method of the photocatalyst provided in this comparative example is basically the same as that in Example 1, except that ethylene glycol is replaced with an equal volume of choline chloride, that is, the raw materials do not contain ethylene glycol.

[0096] Comparative Example 2

[0097] The preparation method of the photocatalyst provided in this comparative example is basically the same as that in Example 1, except that choline chloride is replaced with an equal volume of ethylene glycol, that is, the raw material does not contain choline chloride.

[0098] Comparative Example 3

[0099] The preparation method of the photocatalyst provided in this comparative example is basically the same as that in Example 1, except that choline chloride-ethylene glycol is replaced with an equal volume of water, that is, the raw materials do not contain choline chloride and ethylene glycol.

[0100] The BET data of the composite photocatalyst were measured using a Micromeritics 3020 fully automated surface area and porosity analyzer, and the average particle size was found to be 1429 nm.

[0101] Comparative Example 4

[0102] The preparation method of the photocatalyst provided in this comparative example is basically the same as that in Example 1, except that the molar amount of ferric nitrate is replaced with 1 mol and the molar amount of nickel nitrate is replaced with 2 mol.

[0103] Comparative Example 5

[0104] The photocatalyst provided in this comparative example is α-Fe2O3.

[0105] Experimental Example

[0106] The composite photocatalysts prepared in the above embodiments and the photocatalysts prepared in the comparative examples were used to conduct photocatalytic methylene blue experiments on methylene blue solution. After the photocatalytic methylene blue experiments were completed, the photocatalysts were recovered, and the removal rate and recovery rate of methylene blue solution by each group of photocatalysts were obtained. The results are shown in Table 1.

[0107] The test method for the photocatalytic methylene blue experiment is as follows: 100 ml of a certain concentration of methylene blue solution is transferred; the initial concentration of the methylene blue solution is measured without adjusting the pH value of the solution; 100 mg of the weighed photocatalyst is added to the methylene blue solution, and the treatment is started with light irradiation and stirring, and the time is started; 5 ml of solution is taken every 30 min, and after centrifugation and magnetic separation, the concentration of the supernatant is measured to observe its change over time; within 10 h, the removal rate of each photocatalyst to the methylene blue solution is calculated, and the photocatalyst is separated with a magnet. Then, the regenerated photocatalyst is recovered by alternate washing with anhydrous ethanol and distilled water, and the recovery rate of the photocatalyst is calculated.

[0108] Table 1. Removal rate and recovery rate of methylene blue solution by each group of photocatalysts.

[0109] Group Photocatalyst removal rate of methylene blue solution / % Photocatalyst recovery rate / % Example 1 98 96 Example 2 98 98 Example 3 92 94 Example 4 85 92 Example 5 86 92 Example 6 90 91 Example 7 89 89 Example 8 72 97 Example 9 99 98 Example 10 94 97 Comparative Example 1 48 55 Comparative Example 2 16 46 Comparative Example 3 16 49 Comparative Example 4 68 51 Comparative Example 5 5 0

[0110] The curve showing the change in the removal rate of methylene blue solution by the composite photocatalyst prepared in Example 1 over treatment time is shown below. Figure 2 As shown in the figure. The curve of the removal rate of methylene blue solution by the composite photocatalyst prepared in Example 7 as a function of treatment time is shown in the figure. Figure 3As shown in the figure. The curve of the removal rate of methylene blue solution by the composite photocatalyst prepared in Example 8 as a function of treatment time is shown in the figure. Figure 4 As shown in the figure. The curve of the removal rate of methylene blue solution by the composite photocatalyst prepared in Example 9 as a function of treatment time is shown in the figure. Figure 5 As shown in the figure. The curve of the removal rate of methylene blue solution by the composite photocatalyst prepared in Comparative Example 1 as a function of treatment time is shown in the figure. Figure 6 As shown in the figure. The curve of the removal rate of methylene blue solution by the composite photocatalyst prepared in Comparative Example 2 as a function of treatment time is shown in the figure. Figure 7 As shown in the figure. The curve of the removal rate of methylene blue solution by the composite photocatalyst prepared in Comparative Example 3 as a function of treatment time is shown in the figure. Figure 8 As shown.

[0111] As can be seen from Table 1, the composite photocatalysts prepared in each embodiment have a higher removal rate of methylene blue solution, while the photocatalysts prepared in each comparative example have a lower removal rate of methylene blue solution.

[0112] Furthermore, the composite photocatalysts prepared in each embodiment have a high recovery rate and can be reused.

[0113] Furthermore, the composite photocatalyst recovered in Example 2 was used to continue the photocatalytic methylene blue test, and the recovery was repeated three times. A comparison of the methylene blue removal rate versus treatment time for the first photocatalytic methylene blue test and the three repeated recovery tests using the composite photocatalyst provided in Example 2 is shown in the graph. Figure 9 As shown in the diagram, the third recovery of the composite photocatalyst is as follows: Figure 10 As shown. By Figure 9 It can be seen that even after the third recycling, the composite photocatalyst still exhibits a high removal rate of methylene blue. Figure 10 It can be seen that the recovery rate of the composite photocatalyst in the third recovery is still relatively high.

[0114] Furthermore, the hysteresis loop diagram of the composite photocatalyst prepared in Example 2 is shown below. Figure 11 As shown. By Figure 11 It can be seen that the composite photocatalyst prepared in Example 2 has high coercivity and high saturation magnetization, indicating that the composite photocatalyst prepared in this invention has strong magnetism.

[0115] In summary, the composite photocatalyst prepared by the method provided in this invention exhibits significant removal efficiency for methylene blue, achieving high initial concentration and high removal rate in the methylene blue dye solution. Furthermore, the composite photocatalyst demonstrates excellent magnetic separation and recovery performance (the time required to achieve a 98% photocatalytic removal rate in the first experiment was 120 min, the recovery time was 150 min in the first experiment, 270 min in the second experiment, and only 300 min in the third experiment). The removal rate remains essentially unchanged during repeated use, with only a slight decrease in removal speed. Moreover, the preparation method of the composite photocatalyst provided by this invention is low-cost, energy-saving, and easy to operate, and can be widely applied to the treatment of colored wastewater.

[0116] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A method for preparing a composite photocatalyst for removing methylene blue, characterized in that, Includes the following steps: A mixed solvent containing choline chloride, ethylene glycol and water, a nickel source, an iron source and citric acid were mixed and subjected to a complexation reaction. The pH of the reaction system was then adjusted and heated to carry out a self-propagating reaction to obtain the precursor. The precursor is calcined to obtain the composite photocatalyst; The main components of the composite photocatalyst include NiFe2O4, α-Fe2O3 and Ni3Fe; Adjust the pH of the reaction system to a value of 7-10; The molar ratio of iron in the iron source to nickel in the nickel source is 1.6~2.9:1; The ratio of the molar amount of citric acid to the sum of the molar amounts of iron in the iron source and nickel in the nickel source is 1 to 1.5:

1. The calcination temperature is 400~900℃; In the mixed solvent, the molar ratio of choline chloride to ethylene glycol is 0.5~1.5:1.5~2.5; In the mixed solvent, the ratio of the sum of the volumes of choline chloride and ethylene glycol to the volume of water is 18~27:3~12; The temperature of the complexation reaction is 30~80℃.

2. The composite photocatalyst prepared by the method for preparing the composite photocatalyst for removing methylene blue as described in claim 1, characterized in that, The main components of the composite photocatalyst include NiFe2O4, α-Fe2O3 and Ni3Fe.

3. The application of the composite photocatalyst as described in claim 2 in the photocatalytic removal of organic pollutants.

4. The application according to claim 3, characterized in that, The organic pollutant includes methylene blue, and the composite photocatalyst has a removal rate of ≥70% for methylene blue solutions with a concentration ≤30 mg / L.

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